Glaucoma is a degenerative disease of the eye wherein the intraocular pressure is too high to permit normal eye function. As a result, damage may occur to the optic nerve head and result in irreversible loss of visual function. If untreated, glaucoma may eventually lead to blindness. Ocular hypertension, i.e., the condition of elevated intraocular pressure without optic nerve head damage or characteristic glaucomatous visual field defects, is now believed by the majority of ophthalmologists to represent merely the earliest phase in the onset of glaucoma.
Many of the drugs formerly used to treat glaucoma proved unsatisfactory. Current methods of treating glaucoma include using therapeutic agents such as pilocarpine, carbonic anhydrase inhibitors, beta-blockers, prostaglandins and the like. However, these therapies often produce undesirable local effects. As can be seen, there are several current therapies for treating glaucoma and elevated intraocular pressure, but the efficacy and the side effect profiles of these agents are not ideal. Therefore, there still exists the need for new and effective therapies with little or no side effects.
A variety of disorders in humans and other mammals involve or are associated with abnormal or excessive bone loss. Such disorders include, but are not limited to, osteoporosis, glucocorticoid induced osteoporosis, Paget's disease, abnormally increased bone turnover, periodontal disease, tooth loss, bone fractures, rheumatoid arthritis, periprosthetic osteolysis, osteogenesis imperfecta, metastatic bone disease, hypercalcemia of malignancy, and multiple myeloma. One of the most common of these disorders is osteoporosis, which in its most frequent manifestation occurs in postmenopausal women. Prostaglandins such as the PGE2 series are known to stimulate bone formation and increase bone mass in mammals, including man. It is believed that the four different receptor subtypes, designated EP1, EP2, EP3, and EP4 are involved in mediating the bone modeling and remodeling processes of the osteoblasts and osteoclasts. The major prostaglandin receptor in bone is EP4, which is believed to provide its effect by signaling via cyclic AMP. In the present invention it is found that the formula I agonists of the EP4 subtype receptor are useful for stimulating bone formation. WO 02/24647, WO 02/42268, EP 1114816, WO 01/46140 and WO 01/72268 disclose EP4 agonists. However, they do not disclose the compounds of the instant invention.